Journal of Natural Gas Science and Engineering最新文献

A quantitative evaluation of flow property influenced by micro-scale heterogeneities in shale rocks is presented. Micro- and nano-Computed Tomography images of shale rock samples obtained from Mancos, Marcellus and Eagle Ford formations are digitised into entities such as shale grains, organic matter (kerogen), shale minerals, pores and micro-cracks. Numerical computation on selected layers and sub-micron divisions of the geometries is then carried out using a computationally efficient finite-element based simulation algorithms. Parameters such as pore-volume distribution, porosity, permeability and heterogeneity factor within and across layers are computed as part of pre- and post-process operations. The results of these flow properties characterisation indicated that some shale samples have micro cracks while some do not have. Meanwhile, the presence of micro-cracks in the shale samples contributed to the observed wide variation in permeability and porosity. The static characterisation revealed that different shale rock samples will have different morphological properties. The highest variance in permeability within a layer is of magnitude 5 in Eagle Ford while a magnitude of 2 was computed for Mancos perpendicular. However, magnitudes of 1 and 4 are recorded across layers for Mancos perpendicular and Eagle Ford perpendicular respectively. Contrary to existing assumption that heterogeneity at pore-scale is negligible, it is established from the aforementioned analysis that micro-scale heterogeneity can be quantified. Furthermore, through the analysis of variance and root-mean-square values, it was concluded that tortuosity is inversely related to porosity, permeability and their degree of heterogeneity.

The existence of pipeline defects in oil and gas gathering pipelines predisposed the pipeline to rupture under the synergistic effects of local micro–turbulence and electrochemical corrosion. Here, a combination of experimental and simulation methods was proposed to facilitate the investigation of CO₂ corrosion and the mass transfer process in pipeline defects. The corrosion kinetic characteristics of the defect region were clarified by coupling wire beam microelectrode (WBE) and electrochemical impedance spectroscopy (EIS). Additionally, the effect of flow mass transfer on the corrosion of pipeline defects was investigated by using the existing mass transfer models and COMSOL Multiphysics simulations. The results showed that different locations of the pipeline defects exhibited different mass transfer behavior and corrosion variations. The mass transfer process at the bottom of the defect was lower than that in the upper and lower edge of the defect. Furthermore, the bottom of the defect behaved as an anode and corrodes more severely at low flow velocities. The enhanced mass transfer process led to more severe corrosion at the upper and lower edges of the defect at high flow velocities.

Long-distance energy pipeline pass under roads, subjecting them to repeated stress and posing pipeline safety problems. To simulate the effects of vehicles driving over energy transmission pipeline, this paper examines large-caliber buried pipelines in the suburbs. In this study, a mechanical action model of vehicle-soil-pipeline (VSP) interactions to transform the process of a vehicle driving into the dynamic process of a load changing with time in the specified area was created. The VSP model was used to analyze the influence of moving load and position on the structural characteristics of the pipeline section. An equivalent solution method with high precision and high calculation efficiency was proposed. The results showed that as the loading position approaches the pipeline or the load increases, the stress value at the top of the pipeline gradually exceeded the stress value at the bottom of the pipeline and became the area with the maximum stress value. The minimum stress location also changed from the lower half near the pipeline bottom (Point D-135°) to the upper half near the pipeline top (Point B-45°or Point H-315°). Using the polynomial fitting method, the stress values of the maximum points were equivalently converted. Under the premise of considering pipeline safety, the most suitable functional relationship for the moving load equivalent model was obtained.

The dynamic permeability of coal reservoirs is more complicated than that of conventional reservoirs because of the natural cleat system and matrix shrinkage induced by methane desorption. Many permeability models have been built, but each model has its focus, and the theoretical basis used by them vary, which makes it difficult to compare different models. In this paper, the theoretical basis (basic equations and key relations) of widely cited models was summarized and strictly analyzed. Three limitations were found: the double effect of matrix shrinkage on permeability was not been realized, the concept of effective stress was not clear, and a reliable fracture closure equation was lacking to describe the mechanical response of cleats. Corresponding improvements have been made. Firstly, a new porosity-effective stress relation is obtained without introducing new parameters, which can describe the double effect of matrix shrinkage. Secondly, expressions of three effective stresses considering matrix shrinkage are obtained: Biot effective stress controls the bulk volume strain, pore effective stress controls the pore volume strain, and porosity effective stress controls porosity change. Thirdly, an explicit fracture closure equation is introduced to obtain the analytical permeability models considering the mechanical properties of cleats. Finally, based on the above improvements, a new permeability model system is obtained. Compared with previous models by theoretical analysis, the new models are more comprehensive in considering matrix shrinkage, more accurate in using the effective stresses, and include analytical models based on the mechanical property of cleats.

We investigate supercritical CO${}_2$ injection into a sloping saline aquifer and propose a simple relationship to estimate the maximum gas migration distance in the updip direction. The estimate is derived from the system of governing equations for immiscible flow of gas and formation brine. By writing the equations in non-dimensional form, we guess the scaling law for the migration distance at a late stage of CO${}_2$ injection. Then, we verify the scaling law by means of 3-D reservoir simulations of miscible CO${}_2$ injection with account for the residual and solubility trapping. We derive an estimate that relates the maximum migration distance with the dip angle, the porosity, the anisotropic permeability, and the end-points of saturation functions. We show that the estimate is rather accurate for different reservoir temperatures and brine salinity and in the case of a flue gas injection. The proposed scaling is useful for a quick assessment of the risk of CO${}_2$ reaching a potential leakage site in a large regional aquifer. It can also be applied to estimate the propagation of the uncertainties of reservoir parameters to the uncertainty of the migration distance.

Gas hydrate formation and dissociation have been extensively studied in past decades after introducing hydrate-based technology in the energy and environmental fields. Among all, hydrate-based water desalination (HBWD) has been receiving significant attention because of the shortage in water resources. The present study investigates the equilibrium conditions for gas hydrate formation from propane and carbon dioxide gas mixtures in the presence of pure water and low saline aqueous solutions for the first time. According to the carried out sensitivity analysis on thermodynamic equilibrium conditions of the CO₂+C₃H₈ mixture with different mole fractions of propane (5–50% C₃H₈ + balanced CO₂) it was concluded that the addition of propane above 20% did not significantly affect the hydrate equilibrium condition. Experiments have been carried out with an initial gas molar composition of 20% C₃H₈ and 80% CO₂ in a temperature range of 275.15–280.15 K, at isochoric conditions for the first time. The inhibition effect on the equilibrium conditions is reported in the case of NaCl addition (1, 1.5, 2, and 3 wt%). A reasonable agreement between the experimental data and those calculated from the thermodynamic model applied in this study has been obtained. According to the tests results, the coefficient of determination (R squared) of the final results of the conducted tests and the model predictions are 0.9987 and 0.9950 for pure and saline water, respectively.

In this study, the severity of slugging is assessed by predicting maximum slug lengths (MSL) quickly using the random forest (RF) algorithm based on the geometric features of well trajectories for a shale gas field. Severe slugging is one of the critical issues production engineering-wise because it causes operation shut-down. Thus it should be predicted for proactive measurements. A total of 5033 well trajectories were acquired from the northeastern area of British Columbia, Canada. The well trajectories are described using ten geometric features such as X, Y, and Z lengths in the Cartesian coordinate system, inclination, azimuth, and the other five. The 5033 well trajectories are grouped using the k-medoids clustering algorithm. The well trajectories in each group and the groups are compared visually to see if the ten features are representative enough to describe the geometric features of the well trajectories. The ten geometric features of the well trajectories are used as the input for RF, and MSL, which represents the severity of slugging, is used as the output for RF. The output data is simulation results by a pipe flow simulator, OLGA. The trained RF model provides the satisfactory prediction performance of MSL (R values, 0.866 and 0.857 for training and test data, respectively). In the trained RF model, X, Y, and Z lengths have the most significant importance among the ten geometric features. Because it is impractical to simulate all well trajectory scenarios by OLGA, the MSL values are projected onto a 3-dimensional map of which axes are X, Y, and Z lengths to visualize the trend of MSL. The 3-dimensional map showing the relation between MSL and the geometric features of well trajectories can be utilized as a quick reference to avoid severe slugging in designing well trajectories.

As global energy demand keeps rising, natural gas is meant to be the main protagonist of the clean energy transition, with increasingly importance in power generation and production of chemicals. However, the presence of contaminants in the raw gas, such as H₂S and CO₂, is the cause of several operational and technical issues ranging from equipment corrosion, fouling, catalyst deactivation, and environmental pollution. Therefore, it is necessary to remove contaminants from these gaseous mixtures for their efficient and safe use in multiple applications. The objective of this review is to explore different aspects of the acid gas removal (AGR) processes and technologies. The design of AGR unit and the main parameters affecting the process have been discussed. In the first part, the chemical absorption processes are summarised, including the chemical mechanisms involved and a screening of the main amine-based solvents currently used in such processes. In the second part, the physical absorption processes are presented, with properties, advantages and disadvantages of the typical absorbents. The comparison of various solvents, towards H₂S and CO₂ removal techniques, has been discussed and supported by simulation and experimental studies. Industrial applications of AGR processes have been included in the discussion. Finally, the future directions of research to improve the removal processes and materials have been indicated.

Electromagnetic (EM) methods have provided an alternative means of detecting and estimating gas hydrate, especially in places where hydrates have been established to exist but the gas hydrate shows no bottom-simulating reflection. However, most EM numerical studies being done focused on surface/seafloor Controlled Source Electromagnetic (CSEM) studies with little consideration for borehole EM studies. The assessment and interpretation methods of data from EM surveys require fast and accurate forward modelling algorithms integrated with the complexity of the earth's geological formation. This study develops 2D and 3D anisotropy forward modelling codes using a high-order finite difference frequency domain (FDFD) method for borehole surface EM studies. The newly developed numerical codes can model the effects of anisotropy on borehole-surface earth responses using gas hydrate models. The simulation results revealed that the newly developed numerical codes are highly efficient and suitable for simulating borehole surface CSEM data, especially for marine gas hydrate exploration and other complex earth models. An increase in the coefficient of anisotropy resulted in an increase in the magnitude of the electric field at the surface for the x and z components. Changes in layer resistivity affect the EM field diffusion, recorded Borehole Surface Controlled Source Electromagnetic (BSCSEM) responses, and the overall data interpretation. Also, amplitude of the 3D simulation response increases in the anisotropic faulted earth systems. Lastly, the results imply that Borehole Surface Electromagnetic (BSEM) simulation results can assist with the location and extent of gas hydrates in subsurface.

Polymeric membranes with metal-organic frameworks (MOFs) holds great potential for gas separation. However, finely tailoring the adhesion between MOFs and polymer matrices is crucial in reducing the membranes defective structure. The partial inorganic structure of MOFs limits the interaction with the polymer matrix, which tends to agglomerate on the membranes. Herein, an interfacial strategy is reported by post-synthetic functionalization of MIL-53 (Al) with ionic liquids (ILs) to construct IL@MIL-53 (Al) composite to improve interfacial interaction among filler and polysulfone (PSf) matrices. At 2 wt% of IL@MIL-53 (Al), the composite membranes tensile strength and % elongation were enhanced by about 66.13 and 97.40% compared to the neat PSf membrane. The intimate contact between IL@MIL-53 (Al) and PSf matrices renders uniform dispersion evident from morphological studies. The gas permeation properties were evaluated for carbondioxide (CO₂), nitrogen (N₂), methane (CH₄) gases. At 2 wt% of MIIL-53 (Al) nanofiller, the CO₂ permeance was found to be 37.56 ± 0.63 GPU which was significantly higher than the neat PSf membrane. Besides, the CO₂ permeance of the PSf/2% IL@MIL-53 (Al) membrane was noted to be 34.23 ± 0.68 GPU, whereas the CO₂/CH₄ and CO₂/N₂ selectivities were 48.64 and 49.19% higher than the neat membrane. As the pressure increased from 2 to 10 bar, the CO₂, N_2, and CH₄ gas permeances in composite PSf membranes were decreased, whereas the CO₂/N₂ and CO₂/CH₄ selectivities were observed to be increased. The introduction of ILs into the MOFs pores will tune pore size with the enhanced adsorption selectivity due to its high CO₂ solubility and affinity of ILs. ILs functionalization on the cores of the MIL-53 (Al) structure is an effective strategy, which opens up the selection to a broad range of fillers in the aspect of commercialization.